Whirly Tunes

Design

This is the largest instrument I have ever played, and the only instrument I have built to date. It all began as a simple idea: if you spin a corrugated tube fast enough, it starts producing a pitch. Attach a couple of those to a motor, make multiple of these modules, and tune each one to a single note. Voilà, you have a full chromatic octave of natural harmonics (and another octave of second harmonics above).

The resulting timbre is very unique, somewhere between a choir, an organ, and an angry ceiling fan on top of the quiet but present metallic gearbox hum. The sheer size of the instrument would surprise anyone who sees it for the first time and visually attractive spinning colorful tubes complete the whole experience, turning the encounter into a mesmerizing visual spectacle that leaves an impression.

Initial tests were performed using a stepper motor, which provided us with vital data about speed and power required to spin the corrugated tubes. Thus, we were able to select a suitable geared brushed motor, and obtain twelve of them for a college student-friendly price. The motors were connected in groups of four into one smarter module that had a Raspberry Pi Pico as its brain performing PID control and reading encoders, and two H-bridges as the muscle.

The Performance

In the following project article on Making Music with Machines and Musical Robotics at WPI, videos of the performance are included.
Needless to say, it worked great! Our team of four had to pull a couple long nights, but overall the project was a success, it responded quickly to MIDI keyboard input, and could play almost two full octaves. The natural harmonics turned out to be quiet and easily drowned in the omnipresent mechanical hum. Next time, we should definitely go brushless, but that elevates to a different cost bracket.

Click here to view the project article